Centrifugal casting machine



Aug. 23, 1949. J. FREI, JR

CENTRIFUGAI.

CASTING MACHNE 4 Sheets-Sheet 1 Filed Jan. 20, 1945 NVENTOR. kfOU/ezg?,

Aug. 23, 1949. J. FREI, JR 2,479,610

CENTRIFUGAL CASTING MACHINE Filed Jan. 20, 1945 4 Sheets-Sheet 2 J. FREI, JR

CENTRIFUGVAL CASTING MACHINE Aug. 23, 1949.

4 Sheets-Sheet 5 Filed Jan. 20. 1945 INVENTOR. @hn/Wag J7".

l BY E 7 Q/z Aug. 23, 1949.

J. FREI, JR

Filed Jan. 20, 1945 CENTRIFUGAL CASTING MACHINE 4 Sheets-Sheet 4 INVENToR,

@OLn/ez), kf;

BY /Wwwpum Patented Aug. 23, 1949 UNITED STATES PATENT V-OFFICEQ CENTRIFUGAL CASTING MACHINE John Frei, Jr., Chicago, lll.

Application January 20, 1945, Serial No. 573,745

(c1. zz-cs) claims. 1

This invention relates to machines for use in with centrifugal casting machines.

Centrifugal casting is used in the dental profession for casting inlays and other small parts. and in the jewelry art for casting rings and like small articles. While present day centrifugal casting machines are well suited for casting small articles of precious metals, which bring correspondingly high prices, they are not well suited for commercial production of articles cast of nonprecious metals or alloys, or of appreciably greater size than nger rings. Further, in present day centrifugal casting machines of the character referred to, diflculty frequently is encountered in maintaining the casting metal in proper molten condition until it is projected into the mold, and the use of rubbing contacts for conducting electric current to the heating element of the crucible, where used, gives rise to complications and frequently unsatisfactory results caused by ineilicient contact or failure of parts.

My invention is directed to a centrifugal casting machine of simple construction and operation, which avoids the diiliculties of the present machines above referred to and is particularly suitable for the centrifugal casting of articles on a production basis. More particularly, I provide a rotating bar carrying a crucible and a cooperating mold, and a heating element movable into position eiective for heating and thereby melting the metal or casting material in the crucible, the heating element being also movable into a position clear of the crucible and of the bar and the parts carried thereby, during rotation of the bar. I also provide means whereby the heating element, preferably an induction coil, is energized and deenergized responsive to movement thereof to and from heating position, which is conducive to increased speed of operation, an important consideration in commercial production. I provide power means for rotating the bar and control means therefor whereby the power means is eiective only when the heating element or coil is in position clear of the crucible, the control means being of such character that it has to be held in predetermined position to enable operation of the power means, the latter being disabled upon release of the control means. That provides a safeguard against injury or damage in the event anything goes wrong during the casting operation. In that connection, also provide braking means for quickly stopping rotation of the arm, in the event of a mischance during casting, or stopping it more slowly at the casting articles and has to do more particularly v end of the casting operation. As a further sateguard, I provide means whereby the heating element or coil is automatically and releasably locked in its several positions of adjustment, except its drive position in which the power drive means is enabled. Further objects and advantages of my invention will appear' from the detail description.

In the drawings:

Figure 1 is an isometric side view of a centrifugal casting machine embodying my invention;

Figure 2 is a planview of the machine of Figure 1;

Figure 3 is a sectional view taken substantially on line 3-3 of Figure 2, certain parts, including the mold and associated parts and the supporting arm, being shown in elevation;

Figure 4 is a sectional view, on an enlarged scale, taken substantially on line 4 4 of Figure 2;

Figure `5 is van isometric underneath view of the cover of the main supporting arm, on an enlarged scale; i

Figure 6 is an isometric top view of the main supporting arm and associated parts, with the cover removed and certain parts broken away on the same scale as Figure 5; 1

Figure 7 is a sectional view taken substantially on line 1-1 of Figure 6, on an enlarged scale, with certain parts shown in elevation; l

Figure 8 is a fragmentary isometric side view of the upper portion of the machine of Figure 1, showing the crucible disposed for positioning thereabout of the induction coil; and

Figure 9 is a circuit diagram indicating the controls and associated elements.

I have illustrated my invention, by way of example, as embodied in a centrifugal casting machine comprising a base I0, in the form of a hollow cylindrical casing of refractory masonry construction. A spider II is supported by base I0 interiorly and a short distance from the top thereof, this spider carrying on its upper surface a refractory deck I2 in the form of a disc of asbestos. Spider II is provided with a central collar I3 (Figure 3) from which depends a coaxial bearing sleeve I4 carrying at its lower end a cylindrical housing I5. A stub shaft IE is rotatably mounted through sleeve I4 and extends upward beyond collar I3, having a disc I'i secured on its upper head. A bar i8 is carried by disc I1 and constitutes therewith the head of the machine. Bar I8 is formed in two sections, one of which I9 is iixed to disc I1, conveniently byfbolting, for rotation therewith. A plate 20 is bolted or otherwise suitably xed to the inner end portion of bar section I9 and projects inabout the axis of pin 2l being limited, by the i inner end of section i9, to a position extending at right angles to the latter section. The bar section i9 carries a counterweight 25 adjustable lengthwise thereof and is provided at its outer end with a suitable handle 26 extending upward therefrom. The machine head so far described is of known construction and operation and need not be described in greater detail. A circumferentially grooved pulley- 21 is fixed to the under face of disc I1 and receives a belt 28, which may be a round leather belt, anchored to spider il and deck I2 at one end, at 29. This belt 28 passes from its point of anchorage 29 about the pulley 21 thence outward through the wall of base I8,

over a guide pulley 30 mounted on an armv 3l e secured to and depending from an annular top plate 32 of nonmetallic material, conveniently Wood, mounted on the upper end of base Ill. From the pulley 38 belt 28 passes downward to and about a pulley 33 mounted on a block 34 fixed to the oor or foundation supporting base structure I0. The other end of the belt is anchored to a treadle 35 pivoted on block 34. It

ing down or stopping rotation ofthe machine head, as conditions may require.

A drive shaft 36, disposed in underlying coaxial relation to stub shaft I6, is suitably coupled at its lower end to the shaft of an electric motor will be seen that the pul1ey'21 and belt 28 provide means for braking the stub shaft I6 and slow- 31 mounted in appropriate manner at the lower portion or bottom of base structure I8. The motor 31 is connected to a suitable source of electrical energy, preferably under control of a switch, in a known manner, and normally is continuously driven in the use of the machine. The housing I5 encloses an electromagnetic clutch of any suitable known type, which when energized is effective for clutching drive shaft 36 to stub shaft I6, thereby establishing driving connection between lthese twoshafts. Any suitable means other than the magnetic clutch may be provided for establishing and disestablishing driving connection between the drive shaft 36 and the stub shaft I8, though I prefer to use'the magnetic clutch because the magnetic coupling between these two shafts is conducive' to soft or gentle starting of rotation of the head of the machine, avoiding objectionable jerks or jarsy such as might interfere with the accuracy of the casting operation. 1

The pivoted section 23 of bar I8 carries a crucible and a cooperating mold, as fill be understood. To that end a crucible supporting bracket 38 is suitably mounted on bar section 23. This bracket 38 comprises a base plate 39 seating flatwise on the upper face of bar section 23, and .a vertical plate 40 extending upward from the outer edge of plate 39, plate 46 having therein' an open'- ing or slot 4I the inner portion of which is slightly restricted at 42 to provide an inwardly extending flange 43. The lower portion of slot 40 is of semiseating against the -inner face of plate circular shape, the sides of this slot, including the flange element 43, being tangent to the lower portion thereof. The plates 39 and 48 are formed of a refractory nonmetallic material, preferably compressed asbestos, and are secured together in a suitable manner. As shown, the lower base portion of plate l0 straddles bar section 23 and is bolted or otherwise suitably secured to blocks 33 disposed between and also at opposite sides of members il of bar section 23, which blocks ifi are form'ed of a suitable heat resistant nonmetalllc' material. The plate 39 is also secured to the blocks ed, conveniently by means of screws, and is further secured, by screws t5, to a block i6 fitting snugly but not tightly between the two parallel side members 91 of bar section 23. The screws d5 also pass through a clamping plate Q8 bearing against the under sides of members lll, each of the screws having a nut 49 threaded on its lower end. That provides simple and eiiicient means for securing the bracket 38 in adjustment lengthwise of the bar section 23.

`The bar section is further provided, adjacent its outer end, with means for holding the outer end portion of a mold supported at its inner end by bracket 38. A block 5D, which may be a steel block, is suitably secured, as by-bolting, between adjacent side members lll of bar sections 23, as shown more clearly in Figure 4. This block 58 has suitably secured thereto, conveniently by welding, an upwardly projecting arm 5I carry-.- ing a backing plate 52, conveniently in the form 0f a disc, or substantially so. A mold supporting bracket 5,3 seats upon the upper face of block 50, from' which it extends upward with its outer face 52. Bracket 53 is provided with an inwardly extending base flange 54 clamped between an overlying plate 55 and thev underlying block 50, to which plate 55 is secured in a suitable manner, conveniently by means of screws 56. The bracket 53 is provided, in the inner portion of the vertical arm thereof, with a vertical slot 51 open at its upper end and of substantially semi-circular shape at its lower end. This slot 51 is adapted for reception of the outer end portion of a cylin- `drical mold, as will be explained more fully later.

The bracket 38 is adapted for reception of a Crucible 58 disposed in cooperating relation to the mold 59 supported at its inner end by bracket 38 and at its outer end by the bracket 53. The crucibleand the mold are disclosed in detail in my copending application for Casting mold and method, Serial No. 562,708, filed November 9, 1944, now abandoned and my copending application for Crucible holder and Crucible, Serial No. 573,746, led January 20, 1945, now matured into Patent No. 2,462,259 and a brief description thereof will suffice here. The crucible 58 is formed of a suitable refractory material and comprises upper and lower sections 69 and 6I, respectively, each: of semi-cylindrical cross-section and each provided at its inner end with a peripheral flange 62 having therein an outwardly opening groove 63. Interiorly the crucible 58 defines a suitable recess or heating chamber 64 the outer portion of which converges outward to an opening 65 through the outer end of the mold centrally thereof. The lower section 6I preferably is provided with an upwardly extending flange 66 about the recess therein, the upper section having a downwardly extending flange 61 tting about flange 66.- The upper section 6I) is further provided With an observation opening 68 through its inner end wall. Preferably lower mold section 6I is provided, in the recess thereof, with lengthwise spaced ribs 69 upon which seats an inner crucible or liner 10. also of suitable refractory material. the outer end portion of which tapers outward and opens through a restricted neck 1| extending through opening 65. Theiinner vcrucible 10 is adapted for reception of the metal. alloy or other material from which the articles are to be cast. conveniently in the form of a block or cube 12 of suitable mass or volume for the article to be cast. 1f the inner crucible 10 is not used, the ribs 89 of the lower crucible section 9| may be omitted. the crucible 58 being then the primary crucible. The crucible 58 is mounted in the vertical flange or arm 40 of bracket 38, with flange I3 thereof engaging snugly into the grooves 83 of the flanges 82 so as to hold the crucible sections 80 and 6| in proper register and support the crucible as a whole in horizontal position extending from the mounting means or bracket 38 inward of bar sec tion 23 spaced thereabove.

The mold 59 comprises a cylindrical flask 18 formed of a suitable heat resistant alloy, such as stainless steel. This flask 13 contains a body of refractory 14 having formed therein a casting cavity 15 corresponding to the article to be cast, this cavity opening at its inner end into anfinner gate 16 of substantially conical shape aring inward of the mold. The gate 16 opens, at its outer end, through a strainer element 11, into an inwardly'iiaring outer gate 18, also of substantially conical shape, which opens through the inner end of the mold. The mold seats at its outer end in the bracket 53 and at its inner end in the bracket 38, the latter bracket preferably being so adjusted that the inner end of the mold is spaced a short distance from the outer end of the crucible, to permit of removal and replacement of the mold with expedition and facility. The outer gate i8 of the mold is disposed in substantially concentrical relation to the opening 65 through the outer end of crucible 58 so that, upon rotation of the bar i8, molten material is projected from the crucible into outer gate 18 of mold 59 and thence into the mold cavity 15, as will be understood. i

A supporting arm 19, of hollow construction and formed of wood or other suitable insulating material, is secured to top plate 32 and extends inward of base i substantially diametrically thereof in overlying spaced relation to the head of the machine. Arm 19 is provided with a removable cover 80 carrying on its under face a wooden bar 8i extending lengthwise thereof, this bar having a strip 82 of steel secured to its under face, this strip being provided with spaced recesses 89, 84 and 85, shown more clearly in Figure 5. The horizontal portion of arm 19 is of box formation and receives a block 88, also formed of wood or other suitable electrical insulating material, slidably mounted between guide strips 8l' secured to the inner faces of the side walls of the arm. A coil carrying arm 88 is secured to block 88 and extends downward and inward therefrom. A block 99, of a suitable known electrical insulating and heat resistant material, is secured to the lower end of arm 98 and carries a depending induction coil 90 of known type suitably mounted on block 89. The coil 90 is formed of copper tubing and has its terminals connected, by suitable couplings 9|, of known type, to tubular conductors 92 enclosed within insulation for the major portion of their length and constituting high frequency leads 99. The leads 99 extend upward above arm 19 and then outward through head 99 of upright 95 secured to the outer portion of arm 19. The upright 98 supports the leads 98 and the latter possess suiclent flexibilty to permit of adjustment of the coil lengthwise of arm 19 without subjecting the parts to objectionable stresses or offering objectionable resistance to such adjustment. The leads 93 are connected to a suitable source of high tension alternating current, as will be explained more fully later.

Side bars 98 of suitable insulating material, conveniently wood, are securedY to the sides of arm 88 and extend therefrom beyond the inner end of arm 19, the inner ends of bars 95 being spaced apart by a wood block 91 suitably secured therebetween. Handles 98 are secured to bars 98 at the ends thereof remote from arm 88, there also being brackets 99 secured to the latter ends of side bars 96, each providing an arm extending upward toward the arm 19 and an arm extending downward away from arm 19. A shield |00, of asbestos or other suitable material, is mounted upon the upwardly extending arms of the brackets 99 and a second shield |0I, which may also be formed of asbestos, is supported on the lower arms of the brackets 99. The lower shield |0l is cut away at its central portion to accommodate two glass panels |02 and |03 mounted in a suitable frame, of which panel |02 is of clear glass and panel |03 is of colored or dark glass. A platform |04 is supported at the inner end of arm 19 and spaced thereabove, and a block |05 is secured in the end of arm 19 at the lower portion thereof, and extends therebelow, the sidesof this block being suitably notched to receive the bars 96 so as to guide and support them. The bars 96, together with the block 91 and the block 86 constitute a slide which, by means of the arm 88 and associated parts, supports the coil 90 for rectilineal movement substantially radially of the axis about which the head of the machine rotates.

Block 86 carries an upwardly urged spring pressed detent |06 of known type disposed for engagement into the recesses 83, 84 and 85, selectively, of strip 82, for automatically and releasably locking the slide in adjusted position, thereby locking the induction coil 90 in position.

The block 86 is further provided, at each end thereof, with an adjustable abutment in the form of a threaded stud I9? screwing into the block and secured in adjustment by a jam nut |08. The stud |01 at one end (the outer end) of block 8E is disposed to contact the normally projected button |09 of Aa push button switch H0 of knownV type, mounted in arm 19 adjacent the outer end thereof, in the outer position of block 86. The other stud |01, that is, the stud at the inner end of block 99, is disposed to contact the normally projected button iii of a push button switch H2 mounted in arm i9 adjacent the inner end thereof.

Referring to Figure 9, the high tension leads 93 are connected to a high tension alternating cur rent unit lli-3 of known type the operation of which is controlled by switch Ml through the leads i it. The electromagnetic clutch enclosed within the housing i5 is connected to a suitable source of electrical energy by leads M5 and lit, in the latter of which is interposed the switch H2, which controls the clutch. This switch H2 includes a compression spring (not shown) which urges the button iii thereof toward projected position with sufficient force to move the slide 99 inward of arm 19 a pr-oper distance to permit of opening of switch H2, unless the slide is held by hand in its switch closing position, as will be explained more fully presently. in preparing 1 for casting, the crucible 58 and the mold 59 having been properly mounted in the brackets 38 and 53, bar section 23 is swung about pivot pin 2i in position at right angles to bar section |79, and the head of the machine is turned into position to bring pointer l|1, fixed to disc i1, intovregister with a mark H8 on a block it fixed to deck i2 adjacent disc l1. With the parts disposed as stated, the Crucible 56 is disposed coaxially with coil 96. The upper section 6B of crucible 56 is then removed and the metal or other material of which the article is to be cast is placed within the crucible, after which the upper section 6@ is replaced. During this operation, the coil @E3 is held in its neutral position shown in Figure 8, which corresponds to its dotted line position a. of Figure 9, the slide also being in its neutral position, in which it is releasably locked by the detent |66 engaging into the recess d3 of bar di. After the material has been placed in the crucible and the upper section thereof has been replaced, as above, the slide is moved outward so as to bring the coil 90 into its dot and dash line position b of Figure 9, enclosing the crucible 56 for the major portion of its length. The slide is releasably locked in its latter position Aby engagement of detent l06 in the recess 64, and a. nal check is made to assure that everything is in proper condition for casting. The slide is then moved a further distance outward so as to bring the coil 90 into its effective heating position c, indicated by double dot and dash lines, as distinguished from its ineffective position b. In

j position c of coil 90 the stud |01 at the outer end of block 86 has moved the button |09 of switch ||ll into circuit closing position, thus setting the unit ||3 into operation and energizing the coil 90. Also, in position c of coil 90, detent |06 enters recess 85, releasably locking the slide and the coil in position. It will be understood, of course, that the desired adjustments of the slide are eiected by an operator grasping the handles 98.` With the coil 90 in its effective position c, the operator standing at the front of the machine observes the interior of Crucible 58 through the opening 68 in the inner end thereof. The induction coil 90, when energized, acts in a knownmanner to quickly melt the material within the crucible. When the material has been melted to the proper extent, which can readily be determined by observation, the operator grasps handles 98 and moves the slide along the supporting arm 19 away from the crucible until the block 86 is at the inner or forward end of arm 19, in such a position that the stud |01 at the inner end of this block closes the switch ||2, thus coupling the stub shaft I6 to the drive shaft 36 so as to be rotated thereby. That enables the power source' or electric motor 31 with respect `to the head of the machine for rotating the bar and the parts carried thereby, it being noted that at such time the coil 90 is disposed above and spaced from the bar substantially in overlying relation to disc I1 so as to be clear of the bar land of the Crucible 58 and other parts carried by the bar. In order to maintain the driving'connection between themotor and the head of the machine, the slide has to be held manually in its switch closing position indicated in full lines in Figure 9, in opposition to the spring |20 of switch ||2. Preferably, I provide two compression springs between the pairs of guide strips 81, adjacent the forward ends thereof, in position to be placed under compression by the block 86 when the latter is in its forward position. In the event of any mischance during the casting operation, the operator instantly releases the handles 6d, and the block 86 is moved rearward by the spring of switch H2, supplemented by the compression springs |20 if used, so that switch ||2 is opened and stub shaft 86 is declutched from drive shaft 36 and may quickly be `stopped by drawing the belt 22B tightly about pulley 21. That provides a safe guard, as does the means for automatically locking the slide in its various positions of adjustment, except its position in which the switch H2 is closed.

When the stub shaft i6 is clutched to drive shaft 36, as above, the rotation of the machine head rst causes bar section 25 to swing about pivot pin 2l into alignment with bar section t9, and thereafter continued rotation of the bar ii as a. whole causes the molten material to be projected by centrifugal force from the crucible 58 into the mold 5t. After the bar has rotated sufficiently to project the molten metal into the mold and permit initial setting thereof sucient to retain its cast shape, which requires but a short time, the slide is returned to its neutral position, returning induction coil 96 to its neutral position and opening switch H2, after which the stub shaft may be braked so as to be quickly brought to a stand still. The mold 59, with the cast article therein, may then be removed and replaced by a newmold, and a new charge of metal may be placed in the crucible in the manner above described, after which the operation may be repeated. In that manner, the machine may be operated at comparatively high speed suicient to render it practicable for industrial casting of articles on a commercial production basis. It will be understood, of course, that the surrounding wall of the pit, provided at the upper portion of the base structure, serves as an additional safeguard against injury to the operator in the event of breakage of the crucible or of the mold, oci-of leakage of molten metal.

-As above indicated, and as will be understood by those skilled in this art, changes in construction and arrangement of parts of my invention may be resorted to without departing from the field and scope thereof, andvI intend to include all such variations, as fall within the scope of the appended claims, -in this application in which the preferred form only of my invention has been disclosed.

I claim:

1. In a centrifugal casting machine, a base, a substantially horizontal bar mounted on said base for rotation about a vertical axis intermediate its ends, means for mounting a crucible and a cooperating mold on said bar spaced outward thereof from said axis with the crucible extending inward towardsaid axis and spaced for the major portion of its length from said bar, a supporting arm on said base spaced above said bar, a slide adjustable on said arm movable substantially radially of said axis in one direction'into a heating position and in the opposite direction to a neutral position and a drive posii tion, an induction coil carried by said slide disposedto clear said bar and to be positioned about the crucible in the heating position of said slide and clear of the crucible in the neutral and drive positions of said slide, a motor for rotating said bar, means actuated by said slide for energizing and deenergizing said coil responsive to movement of said slide from neutral position to heating position and vice versa, means for releasably securing said slide in its heating and neutral positions, and means actuated .by said slide for establishing and disestablishing driving connection between said motor and said bar responsive to movement of said slide from neutral to drive position and vice versa, said last means comprising means whereby said slide is urged from its drive position toward its neutral position.

2. In a centrifugal casting machine, a bar mounted for rotation about an axis intermediate its ends, power means for rotating said bar, a crucible and a cooperating mold mounted on said bar spaced outward thereof from said axis with said crucible extending from said mold along said bar toward said axis and spaced for the major portion of its length from said bar, an induction coil movable toward said crucible into heating position extending thereabout and away from said crucible into a neutral position and a drive position clear of said crucible andsaid .bar

and parts carried thereby, in the rotation of said bar, automatic means for locking said coil in its heating and neutral positions, means for energizing and deenergizing said coil responsive to movement thereof from neutral to heating position and vice versa, and means for establishing and disestablishing driving connection between said power means and said bar responsive to movement of said coil from neutral to drive position and vice versaV and for urging said coil from drive position toward neutral position.

3. In a centrifugal casting machine, a bar mounted for rotation about an axis substantially perpendicular to said bar, a crucible and a cooperating mold mounted on said bar spaced outward thereof from said axis, said crucible being substantially parallel with and spaced for the major portion of its length away from said bar, an induction coil aligned with said crucible, means for moving said coil in one direction to a heating position extending about said crucible and in the opposite direction to a neutral position and thence to a drive position, said coil when in said neutral position being spaced a substantial distance from said crucible giving access to the latter and when in drive position being spaced a further distance from said crucible and clear thereof and of other parts carried by said bar, in the rotation of the latter, power means for rotating said bar, means for energizing and cle-energizing said coil responsive to movement thereof from neutral position to heating position and vice versa, and means for establishing and disestablishing driving connection between said bar and said power means responsive to movement of said coil to and from drive position.

4. In a centrifugal casting machine, a bar mounted for rotation about an axis substantially perpendicular to said bar, a crucible and a cooperating mold mounted on said bar spaced outward thereof from said axis, said crucible being substantially parallel with and spaced for the major portion of its length away from said bar, an induction coil aligned with said crucible, means for moving said coil in one direction to a heatinglposition extending about said crucible and in the opposite direction to a neutral position and thence to a drive position, said coil when in 10 said neutral position being spaced a substantial distance from said crucible giving access to the latter and when in drive position being spaced a further distance from said crucible and clear thereof and of other parts carried by said bar, in the rotation of the latter, power means for rotating said bar, means for energizing and deenergizing said coil responsive to movement thereof from neutral position to heating position and vice versa, means for establishing and disestablishing driving connection between said bar and said power means responsive to movement of said coil to and from drive position, and means effective in the drive position of said coil for yieldingly urging it from that position.

5. In a. centrifugal casting machine, a base, a substantially horizontal bar mounted on said base for rotation about a vertical axis, means for mounting a crucible and a cooperating mold on said bar spaced outward thereof from said axis with the crucible extending inward toward said axis and spaced for the maior portion of its length from said bar, a slide mounted on said base overlying said bar and adjustable substantially radially of said axis, an induction coil carried by said slide adjustable therewith in one direction to a heating position extending about said crucible and in the opposite direction to a neutral position and thence to a drive position, said coil when in said neutral position being spaced a substantial distance from said crucible giving access to the latter and when in drive position being spaced a .further distance from said crucible and clear thereof and of other parts carried by said arm, in the rotation of the latter, power means for rotating said bar, means actuated by said slide for energizing and deenergizing said coil responsive to movement thereof from neutral position to heating position and vice versa, means actuated by said slide for establishing and disestablishing driving connection be tween said bar and said power means responsive to movement of said coil to and from drive position, and means effective in the drive position of said coil for yieldingly urging said slide from the position it occupies when said coil is in drive position and thereby disconnecting said power means from said bar.

JOHN FREE, Jn.

REFERENCES CliE'iED The following references are oi record in the nie of this patent: 

